Its a very simple formula that
you can figure out with just a little bit of information. First of all you need
to find out a few things. You will need to figure out your gear ratio which is
the rear sprocket divided by the front driver or sprocket. (i.e. you are running
an 11 tooth driver on your clutch and an 88 on your axle gives you an 8 to one
gear ratio.) Next you will need to measure the circumference of your right rear
tire. (Measuring the right rear makes this formula work even if your running
stagger on an oval kart.) The last bit of information you will need will be the
top RPM you turned while on the track.

So lets say that you are running an
11-81 with a top RPM of 13,900 with a right rear tire size of 34.125. We now
have the information needed to figure your real top speed.

Take 81 divided by 11 which gives
you a gear ratio of 7.36. Next divide your tire circumference by your gear
ratio. 34.125 divided by 7.36 = 4.64. This is the number of inches forward your
kart travels for every RPM of the engine. Now take the number of inches forward,
4.64 and multiply that by the top RPM. 4.64 x 13,900 = 64496. Now we must turn
our inches forward into feet forward which is accomplished by dividing 64496 by
12. (12 inches in one foot) This gives us 5374.6666 which rounded up is 5375.
Then we divide that number by 5280 which is the number of feet in one mile. This
gives us the number of feet our kart travels per minute. 5375 divided by 5280 =
1.018. Then multiply that number by 60 (60 minutes in one hour) and we get
61.08. This is our top speed we obtained during that track session. Below is the
formula written out so you can save it and prove to your friends that you are
really going 61 MPH.

Tire circumference divided by
gear ratio, multiplied by top RPM, divided by 12, divided by 5280, multiplied by
60 = MPH!!!!! It's really not that hard now is it? If your still having
trouble figuring this one out, e-mail me your tire circumference along with your
top RPM and your gear ratio and I'll figure it for you. E-mail to gnckent@yahoo.com

This formula is very useful
to use when you want to know how much top speed you gain or lose when changing
gears at the track. You might find that it helps you figure out the best
possible gear for each track you race at. It has definitely helped us!!!